C125 midterm (pre-lab quizzes)

What is the oxidation state of S in H2SO4?

+6

Draw the best Lewis structure of N2O. What is the formal charge of O?

-1

What is the slope if B is plotted on y-axis and A is plotted on x-axis? 5A + 3B = 8

-5/3

Molar heat of neutralization of an acid or base is the enthalpy change for neutralizing one mole of that acid or base. If 0.10 mole NaOH reacted with 0.058 mole of HCl and 4.2 kJ of heat were released. What is the molar heat of neutralization of NaOH (or HCl)?

-72

When measuring the transmittance of digested cereal sample, what is used as blank?

cereal sample without complexing agents

What is the oxidizing agent of the following reaction? NaBr + Cl2 --> NaCl + Br2

cl2

Which of the following is/are the possible methods of deciding which atom in the CN- ion has more negative charge?

both methods mentioned

In the picture of HOMO orbitals generated by Spartan software, the bigger the lobe on an atom in the CN- ion, the _____ available the electrons are of that atom, the ________ the H+ ion will form bond with that atom.

more, more likely

Which of the following transition in a hydrogen atom will end up releasing the highest amount of energy?

n = 3 to n = 2

Which of the following transitions of the only electron in hydrogen atom will emit longest wavelength photon?

n=100 to n=5

What is the driving force for the reaction between carbon dioxide and sodium hydroxide in aqueous solution? (Hint: what happens to carbon dioxide when it dissolves in water?)

neutralization

Draw the best Lewis structure of nitrate ion first and consider resonance structures if there are any. Which one is correct about the bonds in nitrate ion? There is two single bonds and one double bond One bond is stronger than the other two One bond will be shorter than the other two None of the statements are correct All the statements are correct

none of the statements are correct

How should you read the volume of water using a volume-measuring device with meniscus?

read bottom of meniscus

At room temperature, H2SO4 is dissolved in water and the solution becomes much hotter than the initial temperature of the acid and water. Based on the observation, the dissolution (the process of dissolving) of H2SO4

released some heat and has a negative enthalpy change

Based on VSEPR theory, SF4 molecule should have ________ molecular geometry.

seesaw

According to VSEPR theory, molecules generally adopt a structure that

separate electron pairs as far away from others as possible around the central atom of the molecule.

What is the molecular geometry of XeF4?

square planar

In part IIA of thermochemistry experiment, a student unknowingly spilled a few drops of HCl solution. How will the spill affect the molar heat of neutralization?

the molar heat of neutralization will be lower than what it should be.

In y=kx + b, k is

the slope

When intensity of light changes due to sample absorption, which of the following change accordingly?

transmittance

Based on VSEPR theory, SF4 molecule should have ________ electron domain geometry.

trigonal bipyramidal

What is the molecular geometry of carbonate ion, CO32-?

trigonal planar

what is the electron geometry of CO32- ion?

trigonal planar

Which of the following is a strong electrolyte in water? CH3CH2OH AgCl CsOH HF

CsOH

What is the reducing agent in the following reaction? Cu(s) + 2 AgNO3(aq) --> Cu(NO3)2(aq) + Ag(s)

Cu

Which one is correct about the following phase change? A is an unknown substance. A(l) --> A(g)

It is endothermic with positive enthalpy change.

How many moles of NaOH are needed to neutralize 0.99 mol of H2SO4? Keep 2 decimal places for your answer. Hint: Write the balanced chemical equation first!!

1.98

The molar mass of butane (C4H10) is 58 g/mol. If a student measured the molar mass of butane to be 64, what is the % error of the measurement? Use no decimal place when entering the answer.

10

Which would cause more serious burn, 100 C water or 100 C steam (of equal mass)? Why?

100 C steam because condensation of steam is exothermic

Several balloons of He gas are kept at different temperature, but at the same pressure. At which temperature does the gas have the highest density?

100 K, the lower the temp, the higher the density the higher the temp, the lower the density

The only electron in a hydrogen atom moved from n=3 to n=6. What is the wavelength of photon (in nm) being associated with this transition? Use whole numbers of nm without any decimal places, such as "415", "1125".

1093

How many grams are there in 0.2 moles of acetic acid, (CH3COOH, 60 g/mol)? Keep one decimal place for your answer.

12

Ideal Gas Law states that PV=nRT. Which of the following statements are correct? Check all correct answers. -At constant volume, the pressure of a gas is directly proportional to its absolute temperature. -At constant pressure and temperature, the volume of gas is directly proportional to the R value. -At constant volume and temperature, the pressure of gas is directly proportional to its number of moles. -At constant temperature, the volume of a gas sample is directly proportional to its pressure.

-At constant volume, the pressure of a gas is directly proportional to its absolute temperature. -At constant volume and temperature, the pressure of gas is directly proportional to its number of moles.

Inches of mercury (inHg) is commonly used as unit of atmospheric pressure. It indicates the height of Hg (in inch) that atmospheric pressure can support. If atmospheric pressure is 27.8 inHg, what is it in atm? Use decimals (not scientific notation) and 3 sig figs when entering your answer. Given: 1 in = 2.54 cm = 25.4 mm; 1 atm = 760 mmHg

.929

If in one trial of titration, a student used 20 mL of 0.020 mol/L KMnO4 to titrate all the oxalate ion, how many moles of oxalate ions are there in the sample, assuming that all the oxalate ions are completed titrated by KMnO4?

0.001

In an experiemnt, the best-fit-line equation between Absorbance (A, unitless) and concentration (c, mg/mL) is used to calculate the concentration of Fe. Based on the best-fit line equation given below, what is the concentration of Fe if the absorbance is 1.25? A = 851 c + 0.03

0.0014

Keep in mind that the absorbance was plotted on the y-axis and concentration of Fe in mg/mL was plotted on x-axis to get best-fit line equation from the standard solutions. If the best fit line equation is y = 100x +0.01 What is the Fe concentration in mg/mL if the absorbance is 0.39 based on the best-fit line equation? Keep two sig figs for your answer.0

0.0038

How many moles of NaOH are there in 22.5 mL of 0.87 mol/L NaOH solution? Keep 3 decimal places for your answer.

0.019

If a Fe stock solution has a concentration of 1.5 mg/mL, what is the concentration when 2 mL of this stock solution is diluted to 50. mL? Keep 2 sig figs for the answer.

0.06

100.0 mL of 1.00 mol/L NaOH reacted with 61.1 mL of 1.00 mol/L CH3COOH solution and the temperature increased from 20 to 22 C. How many moles of NaOH (or CH3COOH) are neutralized?

0.0611

Which of the following has the lowest concentration of H+?

0.1 M CH3COOH

What is the absorbance if the % transmittance is 57%? Keep 2 sig figs for the answer.

0.24

A 83.0-g metal sample absorbs 151.5 J of heat and the temperature increases from 20.0 C to 25.4 C. What is the specific heat of this metal in J/(g*C)?

0.34

How many moles of NaOH will be needed to neutralize 0.35 mol of H2SO4? The following equation is NON-balanced: NaOH + H2SO4 --> Na2SO4 + H2O

0.7

At constant pressure, density of gas is inversely proportional to its temperature. This is how hot air balloon is floating in air: burning fuel makes inside air temperature higher and density lower; low density air balloon float on high density regular air. What is the density of air in g/L at 75 degree C if the atmospheric pressure is 1.0 atm? The average molar mass of air is about 29 g/mol. Keep two decimal places for your answer.

1.02

What is the rough bond angle in carbonate ion, CO32-?

120

If 16 g of NaCl is dissolved in 100. g of water, what is the percent by mass (mass%) concentration of NaCl in the solution?

13.8

How many unpaired electrons are there in O2?

2

The lines observed in H-lamp are parts of Balmer Series. All these lines are due to a transition from various higher n value to a common n. What is this common lower n value for all these lines? (Hint: the information can be found near the "Calculations" section on page 7-59.)

2

What is the net ionic equation for the following chemical reaction? 2 NaOH(aq) + CO2(g) -->Na2CO3(aq) + H2O(l)

2 OH-(aq) + CO2(g) --> CO32-(aq) + H2O(l)

A student obtained the Rydberg constant to be 2.13*10-18 J. What is the % error of the measurement? Answer as percentage and keep one decimal place. For example, if your answer is 12.5%, please either use 12.5% or 12.5. The fraction 0.125 will NOT be counted as correct answer.

2.2

A student used water displacement method to measure the density of a metal. The average result of five attempts was 2.763 g/mL, and the calculated standard deviation was 0.026 g/mL. How should the result be reported in a "mean +/- st. dev." format?

2.76 +/- 0.03 g/mL

Read the volume of solution in burrette from the file below

22.62

Which of the following glassware produces the best precision in measuring 10 mL of a liquid?

25 mL graduated cylinder with 0.1-mL marks

Deflate Gate was a hot topic before last year's Super Bowl. According to NFL rule, the football used should be inflated no less than 12 psi. Approximately, what is the REAL pressure of air inside a football when it is inflated to 12 psi? Assume the atmospheric pressure is about 15 psi.

27 psi 12 + 15 = 27 psi

Consider the best Lewis structure of CO32-. How many equivalent resonance structures are there?

3

How many sig figs should the result of the following have? Xs are digits that are purposefully not given. 5.6*7.X + 83.X5

3

How many significant figures should the result of the following calculation have? All Xs are digits that are purposefully omitted. They are not multiplication signs. The * is the multiplication sign. 1.2XX5*(13.XX - 10.XX)

3

NO3- has ______ resonance structures.

3

Green line of Hg lamp has a wavelength of 546.1 nm. What is the energy of a photon associated with this green line?

3.64*10-19 J

100. g water, at 20 C, and 100. g copper, at 80 C, are mixed in an insulated calorimeter. Without doing any calculation, predict a reasonable final temperature after thermal equilibrium is reached. Select the best option! Hint: Without looking up the specific heat values of water and copper, students should know that specific heat of water is much higher than that of copper.

30 C

The molar mass and molar heat capacity of aluminum is 27.0 g/mol and 24.3 J/(mol K), respectively. If a 27.0-g Al sample, at 300. K, absorbed 187 J of heat, what is its final temperature?

307

At STP, 0.106 g of a gas sample occupies a volume of 71.3 mL. What is the molar mass of this gas? Keep 3 sig figs for your final answer.

33.3

If we apply the HOMO and LUMO concepts in atomic orbitals, we will have HOAO (Highest Occupied Atomic Orbitals) and LUAO (Lowest Unoccupied Atomic Orbitals). What is the LUAO of Na atom?

3p

A 100-mL sample of Pb initially has a concentration of 12.9 ppm. If this sample was diluted to 300 mL, what is the new concentration in ppm? Keep one decimal place for your answer.

4.3

The bright violet line of Hg lamp has a wavelength of 435.8 nm. What is the energy of the photon associated with this emission line?

4.56*10^-19 J

A pressure gauge was used to measure the air pressure inside a tire. If the pressure gauge reads 26 psi, what is the real pressure in psi of air inside this tire? Assume atmospheric pressure is 15 psi.

41

Which of the following orbitals of H has the highest energy?

4s

If 6 g of NaCl is dissolved in 100. g of water, what is the mass % of NaCl in the solution? Enter your answer with one decimal place, and as a percentage, such as 15.7%, or just 15.7. Do NOT convert percentage into fraction. For example, if you think 30.1% is the correct answer, enter either "30.1" or "30.1%" , but not "0.301".

5.6 -make to sure to add 6 + 100 and then take 6/106

Given: In Atomic Spectra lab, a student obtained his best-fit line equation to be y = 0.29 x + 46.8 when he plotted his Vernier reading on the y-axis and wavelength in nm on the x-axis. Question: If the Vernier reading for a line is 203.5, what is the predicted wavelength of this line in nm? (Keep 4 sig figs with one decimal place.)

540.3

Oxalate ion is used as a ligand in this lab. It is a bidentate ligand. What is the coordination number of Fe in the green compound you synthesized?

6

A water sample with unknown mass absorbed 100.0 J of heat and the temperature increased from 25.0 C to 29 C. What is the mass of this water sample? Specific heat of water = 4.184 J/(gC).

6.0

50.0 mL of 2.00 mol/L HNO3 solution and 50.0 mL of 1.00 mol/L NaOH solution, both at 20.0 degree Celsius, were mixed in a calorimeter. Calculate the molar heat of neutralization of HNO3 in kJ/mol if: (1) final temperature was 27.1 degree Celsius; (2) the mass of the overall solution was 102.0 g; (3) the heat capacity of the calorimeter was 25.0 J/C; (4) and assume that the specific heat of solution is the same as water, 4.184 J/(g C);

64

In this week's experiment, butane gas will be collected in a graduated cylinder over water. Immediately before reading the volume of gas inside the graduated cylinder, the student must:

Ajust the water level of graduated cylinder

Which of the following is NOT an acid? HCl(aq) CH3COOH All are acids H2CO3(aq) HNO3(aq)

All are acids

A student performed four trials to determine the molar mass of butane in Gas Laws lab. The average of the four trials was 68.7 g/mol and the standard deviation was 8.2 g/mol. How should his result be reported in a "mean +/- st. dev." format? Please make sure that you have proper number of sig figs.

69 +/- 8 g/mol

In a coffee-cup calorimeter, 50.0 g hot water at 60.0 C was mixed with 50.0 g cold water at 20.0 C. If the final temperature is 37, what is the heat capacity of the calorimeter in J/C? Specific heat of water is 4.184 J/(g C)

74

Specific heat capacity of water is 4.184 J/(g C). What is its molar heat capacity?

75.3748

How many valence electrons are there in a hydronium ion, H3O+?

8

A solid sample contains both NaOH and NaCl. 0.500 g of this solid sample was dissolved in water to make a 20.0 mL solution and then this solution was titrated by 0.500 mol/L HCl solution. If 20.9 mL of HCl was used to reach the end point, what is the mass % of NaOH in the original solid sample? NaOH + HCl --> NaCl + H2O

83.6

A student tried to measure the density of a metal by water displacement. Before putting the metal in water, the water volume was 10.26 mL. After putting metal in, the total volume increased to 12.42 mL. If this piece of metal has a mass of 21.46 g, what is the density of the metal?

9.935

What is the bond angle in SF6 molecule?

90.0

Butane gas was collected in a graduated cylinder over water in Gas Laws lab. If the water vapor pressure at the given temperature is 2.8 kPa and the atmospheric pressure is 100.9 kPa, what is the pressure of butane in kPa inside the graduated cylinder? Keep one decimal place for your final answer.

98.1

Based on Lewis structures and Valence Bond Theory, which of the following is true?

Both CH4 and H2O have sp3 hybridization on their central atom.

Which of the following are correct about nodal planes in molecular orbitals? There may have more than one correct answers.

Both bonding and antibonding molecular orbitals may have nodal planes. Regardless it is sigma or pi, the antibonding molecular orbitals always have a nodal plane that is perpendicular to the internuclear axis

At constant temperature, the volume of a gas is inversely proportional to its pressure. This is

Boyles law

In Vinegar Analysis lab, the end point is reached when the final drop of NaOH makes the mixture basic, which turn the pH indicator pink. However, if we put the flask on the bench long enough, the pink color may eventually disappear due to a substance in the air. What substance in the air is causing the pink color of pH indicator to disappear?

CO2 to neutralize the small amount of NaOH

The Total Cereal has a Fe concentration of 0.6 g Fe per g of Cereal. However, it is very common for students to get less than 0.6. Which of the following can be contributors to this lower experimental result than the manufacturer listed value? There are three correct answers and find all of them.

Complexing agent was occupied by excess amount of H+ and did not have a chance to complex with Fe Under-digestion of cereal sample Some Fe was lost during a few transfers between glassware

A sample of solid X was dissolved in 200. g of water at 20. C. If the final temperature of the solution was 15. C, which of the following is true about the dissolution of X in water?

Endothermic with positive heat of solution

Idea of single displacement reaction: 1. Stronger metal can displace weak metal or hydrogen out of their compound. 2. Stronger halogen can displace weaker halogen out of their compound. Which halogen element is the strongest?

F2

Equal mass of water and iron are mixed in a perfect calorimeter and allow heat to exchange until thermal equilibrium is achieved. If the initial temperature of water is 20 C, and that of iron is 80 C, which of the following is correct about the final temperature?

It will be between 20 C and 50 C but probably is much closer to 20 C than 50 C

Which of the following has the smallest bond angle? CH4 BF3 BeCl2 NH3 H2O

H2O

In Part IIA of the thermochemistry experiment, Neutralization between HCl and NaOH, what is the limiting reactant of the neutralization reaction?

HCl

A test tube has a colorless aqueous layer of NaI solution and an colorless organic layer of methylene chloride. When a few mL of colorless chlorine water is added to this test tube, the organic layer becomes pink. What is causing this pink color in the organic layer?

I2

A substance has a molar heat of solution of - 1000 kJ/mol. Which of the following is/are correct if 0.5 mol of this substance is dissolved in water? There might be more than one correct answer.

If only considering the heat exchange within the solution, the resulted solution will have a higher temperature. 500 kJ of heat will be released by the substance

Instead of using 10 mL vinegar, a student used 15 mL vinegar for each of his titrations. How would this affect the experimental result of Vinegar Analysis lab?

It would not affect the experimentally determined mass % concentration of acetic acid in vinegar, as long as no other mistakes were made.

Predict products of the following reaction: Cl2 + KI -->

KCl + I2

A=ebc, where A is absorbance, which is unit-less, b is path length that is 1 cm for the cuvette used. If the concentration c uses mol/L, what unit should the extinction coefficient e have?

L/(mol*cm)

Spectator ions are ions from initial reactants that did not participate in net-ionic equation. For reaction between HF and NaOH (see lab manual for reaction equations 6 to 8), what is the spectator ion?

Na+

Predict the product of the following reaction: NaHCO3(aq) + CH3COOH(aq) -->

NaCH3COO + H2O + CO2

Rearrange the following equation to solve for P. (P+a)(V-b)=nRT

P=(nRT/V-b) -a

All of the following molecules have all bonds being equivalent except: NH3 CH4 SF6 PCl5

PCl5

The LUMO of cyanide ion is: (multiple answers)

Pi MO antibonding MO

A quantity that describes how good the experimental data fits a straight line is called:

R square

Red and purple are two lines of hydrogen lamp. Which one is correct when comparing these two lines? Choose all correct answers.

Red line has longer wavelength than the purple one. Red line has smaller energy than the purple one.

Students used two thermometers in Thermo lab. If both thermometers consistently read temperature exactly 1.0 degree higher than the actual temperature, how does this affect the experimental molar heat of neutralization?

Since the temperature differences are used in all caculations, this should not affect the molar heat of neutralization

In Vinegar Analysis lab, at the end point of a titration, there is still a drop of NaOH solution hanging on the tip of burrette. How does this affect the experimental result in this lab?

Since this drop will make the volume of NaOH artificially higher, it will make the experimental result higher as well.

Why is it important to use the same balance for all weighing in Chemical Measurement lab?

So that all weighing done by a student will have the same systemic error, and as a result, a better precision for all weighing.

Check all categories of strong electrolyte. Soluble ionic compounds weak bases Strong acids alcohole

Soluble ionic compounds and Strong acids

PbSO4 is insoluble in water. Predict the observation for reaction 3A, reaction between Pb(NO3)2 and H2SO4:

Some solid precipitate will form.

Acid anhydride are nonmetal oxides that are resulted from oxyacid molecules losing water. For example, losing one molecule of H2O from H2SO4 produces its acid anhydride SO3. Acid anhydride can also combine with water to form the corresponding acids: SO3 + H2O --> H2SO4. This is why sulfur oxides, such as SO2 and SO3, are major sources of acid rain. CO2, a component of air, is an acid anhydride of carbonic acid (H2CO3). Given above knowledge, which one is correct about a sample of pure water after it is exposed to air for a while? Assume the air quality is excellent and there is no pollutant in air.

The water will be slightly acidic (pH < 7).

If, instead of using 10 mL according to the lab manual, a student knowingly used 20-mL aliquot in Chemical measurement, and used 20 mL as the volume for all subsequent measurements and calculations, how would the experimental result be affected?

This change should not affect the measured water density

When a colorless Ba(NO3)2 solution mixes with a colorless Na2SO4 solution:

a precipitate will form

A beaker of NaOH solution is mixed with a beaker of CuCl2 solution. A chemical reaction occurs. What is the driving force for the reaction?

a precipitation

In the Lewis structure of NH3, there is one lone pair on N atom. What orbital will this lone pair on N reside?

a sp3 hybrid orbital

Which of the following is directly proportional to the concentration of a solution sample?

absorbance of light

In Part IIB of the thermochemistry experiment, neutralization of acetic acid and NaOH, what is the limiting reactant of the neutralization reaction?

acetic acid

Which one is correct about the reaction yield of K3[Fe(C2O4)3]*3H2O? The theoretical yield must be calculated through stoichiometry. all of them are correct. The mass of green crystal collected is the actual yield. Percent yield is the fraction of theoretical yield that was actually obtained, or %Y = (actual Y) / (theoretical Y) * 100%

all of them are correct

Masses (in g) and volumes (in mL) of different amounts of an unknown liquid were plotted in Excel. What is the physical meaning of the slope of the obtained best-fit-line equation?

density

N=N-O and N=O=N are resonance structures to each other. True or False

false

Since we can only see visible lines from a hydrogen lamp, hydrogen lamp does not produce any UV light.

false

Predict the primary driving force of the following reaction: HCl(aq) + NaF(aq) --> HF(aq) + NaCl(aq) Hint: HCl is a strong acid, but HF is a weak acid.

formation of a weak electrolyte

Which of the following might be a contributing factor to low experimental purity of green crystals?

forming the crystals too quickly by cooling it down in an ice-water bath

Evaporation of water __________. (Choose all correct answers.)

has positive enthalpy change AND is endothermic